Gyroscope And Fabrication Process

ABSTRACT

Gyroscopes are sensors that measure angular rate and angular orientation. A three-dimensional fused silica micro shell rate-integrating gyroscope is presented. One aspect of the gyroscope includes the use of optical sensors to detect motion of the resonator. The proposed gyroscope is attractive because it achieves several magnitudes higher accuracy as well as high vibration and shock insensitivity from a novel resonator design as well as other unique manufacturing processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/301,066 filed on Feb. 28, 2016. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to a gyroscope and its fabricationprocess.

BACKGROUND

Gyroscopes are sensors that measure angular rate and angularorientation. Gyroscopes are being adopted in many applications includingconsumer electronics, machines, robots, automotive, vessels, andairplanes, and space satellites. Recent advance in microelectromechanical system (MEMS) technology allowed the manufacturing ofmicro scale gyroscopes at low cost with sufficient accuracy. They arevery useful for applications such as game controllers or smart phones aswell as stabilization of cameras, factory machines, and cars.

However, accuracy of current micro gyroscopes cannot meet therequirements of many other applications. Examples of those include thenavigation of humans, autonomous cars, and drones in regions where noGPS signal is available. Navigation requires precise accurate positionsensing, which is highly difficult. This is because an error in theposition calculated by inertial sensors grows nearly exponentially withtime. Stabilization of cameras, cars, or machines require only rotationrate data, whose error does not grow over time. Therefore, navigationalapplications require a micro gyroscope with several orders of magnitudehigher accuracy than stabilization applications.

This section provides background information related to the presentdisclosure which is not necessarily prior art.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A three-dimensional micro shell rate-integrating gyroscope is presented.The gyroscope includes: a support substrate; an inner shell attached tothe substrate; and a resonator disposed in the inner cavity and mountedon the top surface of the support substrate. The inner shell and definesan inner cavity between an interior surface of the inner shell and a topsurface of the support substrate. Two or more driving electrodes areformed on the support substrate and are arranged around periphery of theresonator. The two or more driving electrodes are configured to drivethe resonator electrostatically. A plurality of optical sensors areintegrated into the support structure, such that each optical sensor isconfigured to detect motion of the resonator.

In one example, the resonator has a hollow hemispherical shape with afirst integral stem extending from a center of an inner surface of theresonator and attached to the support substrate. The resonator may alsoinclude a second integral stem extending from a center of an outersurface of the resonator and attached to the interior surface of theinner shell.

In one aspect, the resonator has a thickness with a minimum valueproximate to a rim of the resonator, such that the thickness of theresonator increases from the minimum value to a maximum value at thecenter of the resonator and the rim of the resonator has a thicknesslarger than the minimum value.

In another aspect, the resonator has a conductive coating disposed on anexterior surface thereof and adjacent to rim of the resonator. Theconductive coating may be patterned as a ring on the exterior surfaceand proximate to the rim of the resonator. Alternatively, the conductivecoating may be patterned as a plurality of discrete electrodes disposedaround a circumference of the resonator and proximate to the rim of theresonator, where each the plurality of discrete electrodes aligns withone of the two or more driving electrodes.

In some embodiments, the gyroscope is mounted onto a platform and theplatform is enclosed by an outer shell. The platform is thermallyisolated from the outer shell.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1A is a perspective view with a partial cross section of a microshell resonator rate-integrating gyroscope (RIG).

FIG. 1B is a perspective view with a partial cross section of a microRIG without an outer shell.

FIG. 1C is an exploded perspective view of the micro RIG.

FIG. 1D is a cross section view of the micro RIG illustrating anarrangement for the drive electrodes.

FIG. 2 is a cross sectional side view of an alternative embodiment of amicro RIG.

FIGS. 3A-3C are cross sectional views of example resonators which may beused in the micro RIG.

FIGS. 4A-4C are cross sectional views of a resonator illustratingpatterns of the tilting, vertical, and wineglass modes, respectively,for the micro RIG.

FIGS. 5A and 5B are cross sectional views of a resonator having athickened rim with a single stem and a double stem, respectively.

FIGS. 6A-6C are partial perspective view of a resonator with differentconductive coatings.

FIG. 7 is a cross section view illustrating an optical sensing methodsintegrated into the micro RIG.

FIGS. 8A-8G are diagrams depicting an example method for fabricating themicro RIG.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

FIGS. 1A-1D depict an example of a three-dimensional micro shellrate-integrating gyroscope 10 (RIG) constructed in accordance with thisdisclosure. The gyroscope 10 is comprised of a support substrate 11; aninner shell 12; a resonator 13; two or more driving electrodes 14 and aplurality of optical sensors 15. Each of these components is furtherdescribed below.

The inner shell 12 attaches to the substrate 11 and defines an innercavity 19 between an interior surface of the inner shell 12 and a topsurface of the support substrate 11. The resonator 13 is disposed in theinner cavity 19 and is mounted on the top surface of the supportsubstrate 11. In some embodiments, the resonator 13 is encapsulated in avacuum (e.g., pressure <50 mTorr). A high vacuum level is preferable fora resonator 13 to achieve a high mechanical quality factor (Q) byreducing squeeze film damping due to gas molecules.

In the example embodiment, the resonator 13 has a hollow hemisphericalshape with a stem 21 for attachment. In this embodiment, the stem isreceived in a hole formed in an anchor support 20. The anchor support 20is formed on the top surface of the support substrate 11. It isenvisioned that the resonator 13 may be attached in other ways to thesupport substrate 11.

Drive electrodes 14 are used to actuate the resonator, for example usingelectrostatic force. The drive electrodes 14 are formed on the supportsubstrate 11 and arranged around periphery of the resonator 13 as seenin FIG. 1D. In the example embodiment, the drive electrodes 14 have ashape of an arc. The drive electrodes 14 are preferably located aroundthe entire perimeter of the rim of the resonator 13 at a close distance(<100 μm) and spaced at equal angles from each other. Other arrangementsfor the drive electrodes 14 are contemplated by this disclosure.

The optical sensors 15 are configured to detect the motion of theresonator 13. Likewise, the optical sensors 15 are arranged around theperiphery of the resonator 13 and may be integrated into the supportstructure. In the example embodiment, the optical sensors 15 arearranged around the entire perimeter of the rim of the resonator andpositioned underneath the rim of the resonator 13. In one example, theoptical sensors 15 are implemented by a single-mode laser diode and aphotodetector mounted in a recess defined in the support substrate 11.Other arrangements for the optical sensors 15 are contemplated by thisdisclosure.

During operation, the gyroscope 10 operates by driving the resonator 13in the flexural modes, also known as the wineglass modes at a constantamplitude. The oscillating pattern (or the standing wave pattern) isaligned to a constant orientation when the gyroscope 10 is not rotated.However, if the gyroscope is rotated along the yaw axis (=z-axis), theorientation of the standing wave pattern changes by an angle that isproportional to the angle of the rotation for the gyroscope. The angularchange is detected by the optical sensors 15 and the rotational rateand/or rotational angle are calculated from the measured angular change.

The example described above is a gyroscope 10 that is drivenelectrostatically while the motion of the resonator 13 is sensedoptically. Driving and sensing principles are not restricted to thesetwo examples. For example, driving of the resonator can be doneelectromagnetically, piezoelectrically, opto-thermally,opto-mechanically, or thermally. Sensing of resonator motion can be donecapacitively, electromagnetically, piezoelectrically, opto-mechanically,or thermally. Different combinations of the driving and sensingprinciples are contemplated by this disclosure.

FIG. 2 depicts an alternative embodiment of a three-dimensional microshell rate-integrating gyroscope. In this embodiment, the gyroscope 10is disposed on a platform 16 and the platform 16 is enclosed by an outershell 17. In this example, the resonator 13 is formed with two stems 21,22 for attachment. A first stem 21 extends downward from a center of aninner surface of the resonator 13 and attaches to the support substrate11; whereas, a second stem 22 extends upward from a center of an outersurface of the resonator 13 and attaches to the interior surface of theinner shell 12. Except with respect to the differences discussed herein,the gyroscope 10 is substantially the same as gyroscope described above.

In this embodiment, the platform 16 is thermally isolated from the outershell 17. The thermally isolated platform 16 keeps the gyroscope 10 at aconstant temperature regardless of changes in outside temperature. Thistechnique is called ovenization. Ovenization eliminates drift in biasand scale factor due to changes in external temperature, which are twoof the most significant sources of errors for a gyroscope. Ovenizationis done by measuring the temperature of the gyroscope using atemperature sensor, comparing the measured temperature to the targettemperature, and flowing electrical current through a heater to heat tothe gyroscope to the target temperature. In an example embodiment, boththe temperature sensor and heater can be made of a thin film metalpatterned either on the thermally isolated platform 16 or on the supportsubstrate 11. By having a large suspended area, the thermally isolatedplatform 16 can have a large thermal resistivity from outside of thesensor. That is, the gyroscope 10 is thermally-insulated from theoutside environment. As a result, the gyroscope 10 can be heated fastusing a small amount of power.

In the example embodiment, the thermally isolated platform 16 is mountedon top of a leadless chip carrier (LCC) package. The platform 16 may bethermally isolated from the LLC package by multiple supporting beams 25also called bridges. The beams can have many different forms includingstraight, folded, circular arc, etc. The beams are designed to havesubstantially narrower width than the width of the platform in order tohave high thermal impedance to reduce the amount of heat conductionbetween the platform and the LCC package. In combination with the outershell 17, the LCC package encapsulates gyroscope in another vacuum(e.g., <50 mTorr). The inner surface of the outer shell 17 may becovered with a shield 24 to prevent radiation heat loss. Materials for aradiation shield 24 include but are not limited to gold, aluminum, orsilver. The high vacuum and the radiation shield helps the gyroscope tohave a large thermal resistance from the outside of the sensor byreducing energy loss through gas conduction and thermal radiation,respectively.

FIGS. 3A-3C illustrate a few example embodiments for the resonator 13.In FIG. 3A, the resonator 13 has a single solid stem, which is joined toan inner surface of the shell of the resonator 13 at its center. Theshell's thickness gradually increases from the rim to the bottom of theshell (t_(rim)<t_(bottom)) as shown. That is, the resonator 13 has athickness that increases from a rim of the resonator to the center ofthe resonator. Of note, the transition region between the shell and thesolid stem has a smooth curvature. In some embodiments, the curvature ofthe transition region is typically but not limited to 1/100 to ½ ofradius of the rim of the shell. This curvature allows the resonator toendure high shock by decreasing stress concentration at the jointbetween the stem and the shell. In some embodiments, the stem may beformed integral with the shell of the resonator 13.

In FIG. 3B, the resonator 13 has dual solid stems, which are connectedto the center parts of both the inner and outer surface of the shell.Again, the shell has a thickness that gradually increases from the rimto the bottom of the shell (t_(rim)<t_(bottom)). In FIG. 3C, theresonator 13 has two solid stems, which are joined to the center partsof the both inner and outer surface of the shell. However, the resonator13 has uniform shell thickness from the rim to the bottom region(t_(rim)=t_(bottom)). In both case, the transition region between theshell and the solid stem has a smooth curvature.

The proposed resonators 13 can have higher vibration and shockinsensitivity while having similarly high accuracy as conventionalhemispherical resonator gyroscopes. This is because the proposedgyroscopes have higher tilting (f_(tilting)) and vertical deflectionfrequencies (f_(vertical)), i.e. higher stiffness for tilting andvertical deflection, and similar f_(wineglass), i.e. similar flexibilityfor the wineglass mode. The displacement patterns of the tilting,vertical, and wineglass modes are shown in FIGS. 4A, 4B, and 4C,respectively. f_(tilting) and f_(vertical) are determined mostly by thethickness of the shell around the transition region as well as thecurvature of the transition region. f_(wineglass) is determined mostlyby the thickness of the shell around the rim. Since the proposedresonators have gradually increasing shell thicknesses from the rim tothe transition region, they can have higher f_(tilting) and f_(vertical)and similar f_(wineglass) as conventional hemispherical gyroscopes.

FIGS. 5A and 5B show two example micro shell resonators 13 havingthickened rims 51. Both shells have a large local thickness at the rim.However, thickness of the shells rapidly reduces down to a minimum valueproximate to the thick region at the rim. Then, the thickness of theshells gradually increases from that minimum value to a maximum value atthe transition region (i.e., center of the resonator). Thus, thethickness is at a maximum at the transition region.

Thickened rim increases the effective mass (M_(eff)) of the resonator.Effective mass is a key parameter that affects the resolution of agyroscope, also known as angle random walk (ARW∝M_(eff) ^(−1/2)). Anglerandom walk is proportional to important parameter affecting theresolution of a gyroscope. Thickened rim also increases f_(wineglass),which is not desirable due to the reduction of the scale factor of agyroscope. However, f_(wineglass) can be controlled to a reasonably lowvalue when the thickness of the shell below the thickened rim isdesigned to be sufficiently small.

When a micro shell resonator 13 is made from an electrical conductor,there is no need to deposit an electrode layer on top of the micro shellresonator. However, when a micro shell resonator 13 is made from anelectrical insulator and when the resonator is driven or sensedcapacitively, an electrode has to be patterned on the surface of aresonator. As the coverage area and the thickness of the electrodeincreases, wineglass modes' Q drop and the anisotropy between the Q andf of the wineglass modes increases. Both of these changes lead to thedegradation of the angle random walk and bias stability of a gyroscope.

FIGS. 6A-6C depict different electrode patterns that can be used on aresonator 13. A conductive coating is disposed on an exterior surface ofthe resonator and adjacent to the rim of the resonator. In FIG. 6a , theelectrode has a shape of a ring 61 that covers the outer surface of theshell near its rim. The electrical connection to the ring electrode isprovided by one more narrow electrical lines 62 patterned from theanchor to the ring 61. In FIG. 6b , the electrode is formed by aplurality of discrete electrodes 63 disposed around a circumference ofthe resonator 13 and near its rim 51. Each discrete electrode 63 alignswith a corresponding drive electrode. The discrete electrodes 63 arepreferably spaced evenly around the resonator 13. The electricalconnection to the electrodes 63 is provided by the multiple narrowelectrical lines 62 patterned from the anchor to each of the discreteelectrodes 63. The electrode patterns in FIGS. 6A and 6B are useful whena resonator 13 is driven using drive electrodes that are located on aside of the resonator 13. In FIG. 6C, a single electrode 64 is patternedon the underside surface of the rim 51. The electrical connection isagain provided by one or more narrow electrical lines 62 patterned fromthe anchor to the electrode. The electrode pattern in FIG. 6C is usefulwhen a resonator 13 is driven using an electrode that is locatedunderneath the rim of the resonator 13. In any case, the electrodesand/or the electrical lines are preferably arranged symmetrically aroundthe center of the resonator 13.

The material for the electrode needs to have low internal energy loss tomake the resonator to have high Q. Examples of these materials includebut are not limited to highly doped amorphous silicon (deposited usingsputtering, plasma enhanced chemical vapor deposition (PECVD) or lowpressure chemical vapor deposition (LPCVD)), tin oxide (sputtered), andplatinum (deposited using sputtering or atomic layer deposition (ALD)).Other types of materials and deposit techniques are contemplated by thisdisclosure.

Gyroscopes calculate rotation rates and angles by detecting the changesin the standing wave patterns caused by the Coriolis force. The amountof change in the standing wave's amplitude is proportional to a rotationrate. For a micro shell resonator gyroscope to detect very low rotationrate (<10⁻³ deg/h), an amplitude change of a fraction of a picometerneeds to be detected. Detection of such a small amplitude change is verychallenging with existing measurement techniques. To address thischallenge, a compact, ultra-high shock resistant optical motionmeasurement system is presented for a gyroscope, capable of detectingsub-picometer amplitude change.

FIG. 7 shows how an optical detection system 70 can be integrated intothe gyroscope 10. In this example embodiment, a micro shell resonator 71is mounted face down on a transparent substrate 72. A single-mode laserdiode, such as a vertical-cavity surface emitting laser (VCSEL), and aphotodetector are mounted inside the recesses defined on the bottomsurface of the support substrate 72. These devices are placed underneaththe perimeter of the resonator's rim at equal angles.

The optical detection system 70 utilizes the optical feedbackinterferometry (FI) principle. Feedback interferometry, also calledself-mixing or injection interferometry, can measure a target'sdisplacement, velocity, and the distance between the laser source andthe target based on the interactions of laser beams that travel in twodifferent optical cavities. The first optical cavity is a Fabry-Perotcavity of a laser diode, and the second optical cavity is between thelaser diode and the target, that is, the rim of the resonator. As thelaser beam that reflects off from the rim enters the first opticalcavity, the two beams make optical interference. This causes thecharacteristic (intensity, frequency, phase) of laser beam to change.The characteristics of the laser beam are measured using a photodetector at the bottom of the laser source.

Feedback interferometry has several attractive features. First, laserdiodes and photodetectors do not need to be placed at a close distanceto the rim. This is not the case for the capacitive measurementtechnique, because a capacitance has an inversely proportionalrelationship with the distance between the rim and the electrode.Placing a readout electrode at a close distance from the rim ischallenging because the microfabrication process becomes complicated andgyro performance degrades after high shock event due to potentialcollisions between the resonator and the electrode. Second, compared toother interferometry techniques, such as Michelson, Mach-Zehner, andSagnac interferometry, FI requires a simple setup because it does notrequire an external optical interferometer. Therefore, an FI setuprequires a far smaller volume and is more stable against shock andvibration than other methods. The size of a VCSEL is quite small; forexample, relevant commercially available devices from PrincetonOptronics Inc. are only 250×250×110 μm³. Third, FI only requires a laserdiode with an integrated photodetector and optionally a lens. It doesnot require precise alignment or filtering, as the laser naturallyfilters out the relevant spatial mode. Fourth, FI provide very sensitivemeasurement, as the detected signal is always in the quantum regime(except for a small reflectivity loss at the laser diode entrancemirror) and the quantum-limited signal-to-noise ratio is attainable.Fifth, commercially available VCSEL has high wavelength stability, sothe motion detection accuracy is very high. For example, the 0.7 mW, 680nm True Single-Mode VCSEL (PN: 680S-0000-X003) from Vixar has awavelength temperature coefficient of 0.045 nm/° C. and has the optionfor an integrated thermoelectric cooler that brings the λ tolerance downto ±10 pm. The wavelength can be further stabilized by ovenizing thedevice with very high accuracy or locking the laser output to theabsorption line of a rubidium vapor cell. Sixth, FI consumes low energy.Driving eight VCSELs for gyro motion sensing requires typically requirespower less than 10 mW. While reference has been made to a particularoptical detection system, this is merely one aspect of the gyroscopedesign such that other aspects of this disclosure are applicable togyroscopes that employ other types of resonator motion detectionsystems.

Turning to FIGS. 8A-8G, an example method for fabricating thethree-dimensional micro shell rate-integrating gyroscope 10 is describedin more detail. Fabrication can begin with the hemispherical resonator13. The materials for the resonator 13 may include but not limited toborosilicate glass, borofloat glass, aluminosilicate glass, ultra-lowexpansion glass, fused silica, sapphire, ruby, silicon carbide, quartz,and alumina. In one embodiment, the resonator 13 has a radius, height,and anchor dimensions from 100s μm to a few cm. The resonator 13 has asolid anchor post (to provide shock resistance), and a thicknessgradient in the shell wall (to provide vibration resistance), which isthickest in the center and thins down to furthest from the anchor exceptfor the rim as described above. In the example embodiment, the thicknessof the shell is on the order of 10s μm to 100s μm. As described above,the rim 51 of the resonator 13 can be optionally thickened to increaseeffective mass.

First, the resonator 13 is fabricated from a thermally reflowablematerial using a modified blowtorch molding process. An annulus isformed on a surface of a substantially planar reflow material 80 as seenin FIG. 8A. In this example, two concentric annulus 81, 82 are formed inthe reflow material 80. The inner annulus 81 is sized such that it willform the thickened rim after molding while the outer annulus 82 alignswith the edge of the mold to ensure the inner annulus is centered.Another option is to place a separate annulus into the bottom of themold such that the reflowing shell will fuse to it at predefined depthand radius. The fused silica shell may be annealed to relax residualstresses, which has been shown to improve Q.

In FIG. 8B, the reflow material 80 is disposed onto a mold 83. The moldhas a cylindrical recess 84 formed therein and the reflow materialencloses the recess 84. The sidewall of the recess does not have to beperpendicular. Angled or curved sidewalls are also envisioned. The moldfurther includes a protrusion 85 projecting upward from a bottom surfaceof the recess and positioned at center of the bottom surface of therecess. The reflow material 80 is preferably reflowed at a temperatureabove the softening temperature of the reflow material. The reflowmaterial 80 touches and fuses to the solid post 86 mounted inside acylindrical hole formed in a center of the protrusion.

While the reflow material is disposed on the mold, the reflow materialis heated. With reference to FIG. 8C, the reflow material reflowstowards the bottom surface of the recess of the mold, for example withthe help of a pressure gradient created across the reflow material. Thesolid anchor post 86 that is recessed below the top of its surroundingdome, causes the reflow material to flow down and form a smooth, roundedjunction with the post 86. This reduces stress concentration at thatjunction, making the resonator more robust in harsh dynamicenvironments. Further details regarding this reflow process can be foundin an article by J. Cho et al's entitled “A high-Q all-fused silicasolid-stem wineglass hemispherical resonator formed using micro blowtorching and welding” In Proc. MEMS 2015, pp 821-824 (January 2015)which is incorporated herein in its entirety by reference.

The resonator 13 is released from the mold as seen in FIG. 8D. Theresonator 13 is polished through lapping and chemical-mechanicalpolishing, and then selectively coated with a thin conductive layerusing shadow masking. Metal grain slippage during mechanical deflectionis a source of energy loss, so minimizing metal coverage should helpmaximize Q. A thin metal will be selectively coated on the inside of theshell so that a bias connection can be made to the anchor post. For avertical drive scheme, additional metal need only be deposited on thepolished rim, but not on the outside of the resonator. For lateraldrive, the metal must continue to the outer part of the shell that isparallel to the electrodes. Another option is atomic layer deposition ofmetal onto the entire exterior surface of the shell, which has severaladvantages over physical vapor deposition (PVD) that help to increase Q.PVD is non-conformal due to line of sight deposition, creating stressgradients over temperature that degrade Q. It also tends to formmetallic grains, which limits the minimum thickness required for aconductive film. Slippage between grains due to mechanical deflectionalso results in energy loss. Atomic layer deposition can providethinner, more uniform metal coatings, helping to maximize Q.

Next, the support substrate 11 for the gyroscope 10 is fabricated. Inthe example embodiment, the support substrate 11 includes a topsubstrate 91 and a bottom substrate 92 as seen in FIG. 8E. The topsubstrate 91 is typically made by bonding and patterning an electricalsemiconductor (e.g., silicon) or patterning an insulator (e.g., fusedsilica) and coating the sidewalls of the patterned features with anelectrical conductor (e.g., gold or titanium); whereas, the bottomsubstrate 92 is made from an optically transparent, electricalinsulating material (e.g., glass or fused silica). On the bottomsubstrate, an anchor attachment point, multiple drive electrodes,electrical feedthroughs 94, and cavities 93 to contain the eight VCSELsfor optical readout are defined, for example by wet etching, dryetching, sandblasting, milling and drilling. The bottom substrate 92 isthen bonded to the top substrate 91. In the center of top substrate 91,a hole 96 is etched that serves as the seat for the solid anchor post86. A small amount of the material is left under the anchor to ensurethe rim, which is level with the anchor post, does not touch thesubstrate. A circular trench etched down to the glass around the anchorseat electrically isolates the shell. For a lateral drive scheme, thickdrive electrodes 14 are fabricated concentric to the outside of theshell rim with gap for example smaller than <100 μm gap, while for avertical drive scheme, thin electrodes are fabricated to align with thepolished rim, at a distance of <100 μm from its surface.

To make electrical connections to the electrostatic drive electrodes 14,deep trenches are etched through the glass side to reach the bottom ofthe electrodes, thus maintaining a hermetic seal. The trenches are thenrefilled with metal by electroplating. Square holes are etched into theglass in a circular pattern opposite the rim to form cavities for theVCSELs, which are aimed through the glass at the polished rim of theresonator. If necessary, a commercial microlens and appropriate spacermay be placed in the holes below the VCSELs to control beam divergence.VCSELs will be embedded in a polymer, such as Parylene, to fix theirposition and provide some mechanical protection. Metal traces 98 arepatterned on the glass side to contact the drive electrodes 14 and theVCSELs 15 as seen in FIG. 8F.

A lid 99 will be thermally molded to fit over the resonator 13 and itselectrodes as shown in FIG. 8G. If desired, this could incorporate asecond anchor to secure the shell resonator. The dome may be attachedwith glass frit, laser welding, or silicate bonding. While the abovefabrication method has been described with specific components havingspecific values and arranged in a specific configuration, it will beappreciated that this method may be implemented with many differentconfigurations, components, and/or values as necessary or desired for aparticular application. The above configurations, components and valuesare presented only to describe one particular embodiment that has proveneffective and should be viewed as illustrating, rather than limiting,the present disclosure.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

1.-11. (canceled)
 12. A method for fabricating a mechanical resonator,comprising: forming one or more grooves into a surface of asubstantially planar reflow material; disposing the planar reflowmaterial on a mold, where the mold has a recess formed therein and theplanar reflow material encloses the recess, wherein the mold furtherincludes a protrusion projecting upward from a bottom surface of therecess; heating the reflow material while the reflow material isdisposed on the mold; and reflowing the reflow material towards thebottom surface of the recess of the mold by creating a pressure gradientacross the reflow material, thereby forming a resonator microstructure.13. A method for fabricating a mechanical resonator, comprising: formingan annulus on a surface of a substantially planar reflow material, wherethe annulus has a thickness larger than remainder of the planar reflowmaterial; disposing the planar reflow material on a mold, where the moldhas a recess formed therein and the planar reflow material encloses therecess, wherein the mold further includes a protrusion projecting upwardfrom a bottom surface of the recess and positioned at center of thebottom surface of the recess; heating the reflow material while thereflow material is disposed on the mold; and reflowing the reflowmaterial towards the bottom surface of the recess of the mold bycreating a pressure gradient across the reflow material, thereby forminga resonator microstructure.
 14. The method of claim 12 wherein theprotrusion of the mold has a substantially hemispherical shape with acylindrical hole formed in a center of the protrusion.
 15. The method ofclaim 14 further comprises placing a post into the cylindrical hole ofthe protrusion, where reflow material flows into the cylindrical holeduring the reflowing step and bonds with the post, thereby forming anintegral stem.
 16. The method of claim 12 further comprises controllingthe pressure gradient across the reflow material independently fromheating the reflow material.
 17. The method of claim 12 furthercomprises heating the reflow material using a heat source and creating apressure gradient across the reflow material using a vacuum that differsfrom the heat source.
 18. The method of claim 12 further comprisesseparating the resonator microstructure from the mold after the step ofreflowing the reflow material; polishing the resonator microstructure;and coating an exterior surface of the resonator microstructure with ametal.
 19. The method of claim 18 wherein coating an exterior of theresonator microstructure with a metal further comprises patterning thecoating as a plurality of discrete electrodes disposed around acircumference of the resonator microstructure and proximate to the rimof the resonator microstructure, where each the plurality of discreteelectrodes aligns with one of the two or more driving electrodes. 20.The method of claim 12 providing a support substrate; attaching theresonator microstructure to a top surface of the support substrate;forming a plurality of trenches in a bottom surface of the supportsubstrate, such that each of the plurality of trenches is alignedunderneath a rim of the resonator microstructure; embedding an opticalsensor into each of the plurality of trenches such that each opticalsensor is configured to detect motion of the resonator.
 21. The methodof claim 19 further comprises fabricating at least one driving electrodeformed on the support substrate and arranged around periphery of theresonator microstructure, where the at least one driving electrode isconfigured to drive the resonator electrostatically.
 22. The method ofclaim 13 wherein the protrusion of the mold has a substantiallyhemispherical shape with a cylindrical hole formed in a center of theprotrusion.
 23. The method of claim 22 further comprises placing a postinto the cylindrical hole of the protrusion, where reflow material flowsinto the cylindrical hole during the reflowing step and bonds with thepost, thereby forming an integral stem.
 24. The method of claim 23further comprises controlling the pressure gradient across the reflowmaterial independently from heating the reflow material.
 25. The methodof claim 24 further comprises heating the reflow material using a heatsource and creating a pressure gradient across the reflow material usinga vacuum that differs from the heat source.
 26. The method of claim 25further comprises separating the resonator microstructure from the moldafter the step of reflowing the reflow material; polishing the resonatormicrostructure; and coating an exterior surface of the resonatormicrostructure with a metal.
 27. The method of claim 26 furthercomprises providing a support substrate; attaching the resonatormicrostructure to a top surface of the support substrate; forming aplurality of trenches in a bottom surface of the support substrate, suchthat each of the plurality of trenches is aligned underneath a rim ofthe resonator microstructure; embedding an optical sensor into each ofthe plurality of trenches such that each optical sensor is configured todetect motion of the resonator.
 28. The method of claim 29 furthercomprises fabricating two or more driving electrodes formed on thesupport substrate and arranged around periphery of the resonatormicrostructure, where the two or more driving electrodes are configuredto drive the resonator electrostatically.
 29. The method of claim 28wherein coating an exterior of the resonator microstructure with a metalfurther comprises patterning the coating as a plurality of discreteelectrodes disposed around a circumference of the resonatormicrostructure and proximate to the rim of the resonator microstructure,where each the plurality of discrete electrodes aligns with one of thetwo or more driving electrode.
 30. A method for fabricating a mechanicalresonator, comprising: forming one or more grooves into a surface of asubstantially planar reflow material; disposing the planar reflowmaterial on a mold, where the mold has a recess formed therein and theplanar reflow material encloses the recess, wherein the mold furtherincludes a protrusion projecting upward from a bottom surface of therecess, and wherein the protrusion has a circular cross section withrespect to the bottom surface of the recess and includes a hole alignedwith a center of the circular cross section of the protrusion; heatingthe reflow material while the reflow material is disposed on the mold;and reflowing the reflow material towards the bottom surface of therecess of the mold by creating a pressure gradient across the reflowmaterial, thereby forming a resonator microstructure.